The sequel was announced in May 2012, after the successful release of The Avengers. Whedon, the director of the first film, was brought back on board in August and a release date was set. By April 2013, Whedon had completed a draft of the script, and casting began in June with the re-signing of Downey. Second unit filming began in February 2014 in South Africa with principal photography beginning in March. The film was primarily shot at Shepperton Studios in Surrey, England, with additional footage filmed in Italy, South Korea, and various locations around England.
Avengers: Age of Ultron is scheduled for release on May 1, 2015 in North America, in 2D and IMAX 3D.
With S.H.I.E.L.D. destroyed and the Avengers needing a break from stopping threats, Tony Stark creates Ultron, a self-aware, self-teaching, artificial intelligence, who can assess threats and control Stark's Iron Legion. However, things quickly go awry when Ultron decides that humans are the main enemy and sets out to eradicate them from Earth.
A genius scientist who, because of exposure to gamma radiation, transforms into a monster when enraged or agitated. Ruffalo worked with motion capture performer Andy Serkis' The Imaginarium Studios in preparation for the role. Ruffalo added, "[My role's] even bigger than last time, and it's more complex and it has more layers and a bit more arc. Not only that, but it seems that the motion capture process is becoming a whole lot more agreeable second time around. I'm really tripping on the technology of this motion-capture stuff... now I just completely embrace it and see it as this other exciting place we can go as performers." Describing the relationship between Banner and Hulk in the film, Ruffalo said, "I think there’s a whole relationship with Banner and Hulk that needs to be discovered. There’s a very cool thing happening: Hulk is as afraid of Banner as Banner is afraid of Hulk." Ruffalo added, "Both of these guys are obviously the same guy, and they have got to come to peace somehow with each other. And I think that this confrontation is building along the lines of this film."
The co-leader of the Avengers, who is a World War II veteran enhanced to the peak of human physicality by an experimental serum and frozen in suspended animation before waking up in the modern world. Evans said that he was able to maintain the strength he built up for Captain America: The Winter Soldier by working out up to an hour a day. Evans said, "...you pull the plug about two to three weeks before you wrap. When you see the finish line coming, you are so glad to not have to think about the gym. But we are starting Avengers 2, so over the past month, I have been hitting it pretty hard."
A highly trained spy, formerly of S.H.I.E.L.D. Producer Kevin Feige stated that more of the character's backstory is explored in the film. Johansson elaborated, "In Avengers 2 we go back... we definitely learn more about Widow's backstory, and we get to find out how she became the person you see. All of these characters have deep, dark pasts, and I think that the past catches up to some of us a little bit." On where the film picks up Widow's story, Johansson said, "At this stage, when you see the Widow, she's — especially in Avengers, these characters all have a past, and hers [sic] is a very complex one, where she's realizing — and it's kind of a continuation of Cap 2 — 'I've never made an active choice. I'm a product of other people's imposition.' That's going to catch up with her. That's bound to have a huge effect. There's got to be a result of that realization... You'll see her actively making some choices in her life, for better or worse." A mixture of close-ups, concealing costumes, stunt doubles and visual effects were used to help hide Johansson's pregnancy during filming.
A master archer who worked as an agent for S.H.I.E.L.D. in previous films. Whedon said that Hawkeye would interact more with the other characters in the film, as opposed to the first film where the character had been "possessed pretty early by a bad guy and had to walk around all scowly."
The former director of S.H.I.E.L.D. who originally recruited the Avengers. Jackson described the role as a cameo, saying, "I'm just kind of passing by... Because, it's another one of those 'people who have powers fighting people who have powers'. That's why I didn't get to New York in The Avengers. There's not a lot I could do except shoot a gun."
The twin brother of the Scarlet Witch, who can move at superhuman speed. About the character Taylor-Johnson said, "Him [sic] and his sister [Scarlet Witch] have been abandoned by their parents and their father, and they grew up in Eastern Europe defending and looking out for themselves and each other... His sister really is his guidance - emotionally she's the one who looks after him, and vice versa. He's very overprotective physically - he doesn't want anyone touching her." Taylor-Johnson also said that Quicksilver has "real anger frustration" and is easily bored due to a short attention span. Feige stated exploring Quicksilver's relationship with his sister and his backstory growing up in Eastern Europe would help differentiate the character from Evan Peters' version in X-Men: Days of Future Past (2014).
The twin sister of Quicksilver, who can harness magic and engage in hypnosis and telekinesis. Olsen said, “The reason she’s so special is because she has such a vast amount of knowledge that she’s unable to learn how to control it. No one taught her how to control it properly. So it gets the best of her. It’s not that she’s mentally insane, it’s just that she’s just overly stimulated. And she can connect to this world and parallel worlds at the same time, and parallel times.” Olsen drew on her relationship with her older brother and her twin sisters to prepare for the role.
An artificial intelligence programmed with elements of Tony Stark's personality, who is overwhelmed with a god complex and longs to bring peace to Earth by eradicating humanity. Director Joss Whedon stated that Spader was his "first and only choice" for the role, because of his "hypnotic voice that can be eerily calm and compelling" while also being very human and humorous. Feige clarified, "We'll be capturing his face and his body to create a whole performance... We did not hire James Spader to do a robot voice." Extensive scans were taken of Spader's head and body in preparation for the role. About the character Whedon said, "He's always trying to destroy the Avengers, goddamn it, he's got a bee in his bonnet. He's not a happy guy, which means he's an interesting guy. He's got pain. And the way that manifests is not going to be standard robot stuff." Whedon added that Ultron is "not a creature of logic – he's a robot who's genuinely disturbed. We're finding out what makes him menacing and at the same time endearing and funny and strange and unexpected, and everything a robot never is." Whedon also indicated that some of Ultron's abilities from the comics would be stripped.
"I have to make my movie assuming that people will only have seen the first one, or possibly not even seen the first one. I can't assume that everybody went to see Thor [The Dark World], Captain America [The Winter Soldier], and Iron Man  in-between. I have to go from one movie to the next and be true to what's happened, but not be slavish to it... The model I'm always trying to build from, my guiding star, is The Godfather Part II where a ton has happened in-between and it's a very different movie [from The Godfather], but you don't need any information: it's there in the film."
—Joss Whedon, director of Avengers: Age of Ultron, on balancing the film's accessibility and continuity.
In October 2011, Feige said during the New York Comic Con, "Iron Man 3 will be the first of what we sort of refer to as phase two of this saga that will culminate, God willing, in Avengers 2". In March 2012, Joss Whedon, director of the first film, stated that he would want a sequel to be "smaller. More personal. More painful. By being the next thing that should happen to these characters, and not just a rehash of what seemed to work the first time. By having a theme that is completely fresh and organic to itself." At the premiere of The Avengers, Feige said the studio had an option for Whedon to return as director. In May 2012, after the successful release of the first film, Disney CEO Bob Iger announced a sequel was in development. Most of the film's cast members were under contract to potentially appear in the sequel; however, Robert Downey, Jr. was not, as his four picture deal with Marvel expired after Iron Man 3.
At the 2012 San Diego Comic-Con International, Joss Whedon said he was undecided about directing, stating, "I have not come to a decision on directing Avengers 2. I am having too much fun with this [Firefly reunion] now." However in August 2012, Iger announced that Whedon would return to write and direct the sequel and develop the Marvel television series, Agents of S.H.I.E.L.D., for ABC. Later in the month, Disney set a May 1, 2015 release date. When asked about his decision to return, Whedon said, "Avengers 2, it wasn't a tough decision. For a long time I thought, 'Well, it's just not going to happen.' Then when I actually started to consider it, it became so clear that I desperately wanted to say more about these characters, it would've been an easy no and it was a spectacularly easy yes. There was no wrestling." Whedon said that they intended for the film's production to not be as rushed as the first one.
By April 2013, filming was scheduled to begin in early 2014 at Shepperton Studios in England. At the Hollywood premiere of Iron Man 3, Whedon said that he completed a draft of the script, and had started the storyboard process and to meet with actors. Whedon also mentioned that he wrote with Downey in mind and included a "brother/sister act" from the comic books, later confirming that he was referring to Quicksilver and Scarlet Witch. During an appearance on Late Night with Jimmy Fallon, Whedon explained his rationale for including the characters in the film saying, "Besides the fact that I grew up reading them, their powers are very visually interesting. One of the problems I had on the first one was everybody basically had punchy powers... [Quicksilver]'s got super speed. [Scarlet Witch] can weave spells and a little telekinesis, get inside your head. There's good stuff that they can do that will help sort of keep it fresh." Whedon later elaborated, "I fiercely dislike the idea of just throwing in more people for the sake of doing that. Last time I had all of Earth's Mightiest Heroes versus one British character actor, and I needed more conflict." By May, Downey had entered negotiations to extend his contract with Marvel Studios and reprise his role as Iron Man in the film. A month later, Downey signed on to return for the then-untitled Avengers sequel, as well as a third Avengers film.
At the 2013 San Diego Comic-Con International, Whedon announced the film would be subtitled Age of Ultron. Despite the subtitle, the film is not based on the 2013 comic book miniseries Age of Ultron. Feige explained, "We came up with a few titles, but every month a new comic book appeared, and that's a great title. Age of Ultron is a great title. We had a few other 'Of Ultrons', but that was the best one. So we're borrowing that title, but taking storylines from decades of Avengers storylines." Whedon added that Ultron's origin would differ from his comics roots, and that Hank Pym would not be involved with Ultron's creation. Whedon also said the film would have a darker tone due to Ultron's involvement. The title of the film came as a surprise to many fans who were expecting Thanos, the mastermind behind the events of the first film, to be the main villain in the sequel. When asked about Thanos' involvement, Whedon responded, "We have to stay grounded. It's part of what makes the Marvel universe click - their relationship to the real world. It's science fiction, and Thanos is not out of the mix, but Thanos was never meant to be the next villain. He's always been the overlord of villainy and darkness." Commenting on finding the right balance between technology and fantasy based heroes in Avengers: Age of Ultron, Feige said "Iron Man is a very technological hero his movies are always technologically based. The first Thor was all about introducing Asgard and Thor in that more fantastical realm into the more reality-based [Marvel Cinematic Universe (MCU)], and explain that obviously it might look like magic, but it's another form of science and technology. As we go into Ultron clearly he does come out of technology, but we're using all of our tools at our disposal that we've established so far as part of the MCU to build the storyline of Age of Ultron."
On January 24, 2014, the Forte di Bard Association announced that filming would take place at Fort Bard in the Aosta Valley region of Italy in March 2014, as well as other locations in Aosta Valley including Aosta, Donnas, Bard, Pont-Saint-Martin, and Verrès. The next month, the Gauteng Film Commission announced that action sequences would be filmed in Johannesburg, South Africa and other locations in Gauteng, beginning in mid-February. A few weeks later Marvel announced that portions of the film would be shot in South Korea. Feige cited the nation's "cutting-edge technology, beautiful landscapes and spectacular architecture" as ideal for the film.Gyeonggi Province and its capital, Seoul were selected as filming locations with South Korea's Ministry of Culture, Sports and Tourism reimbursing up to 30% of the studio's expenditures, as part of a state-funded incentive program.
Filming began on February 11, 2014 in Johannesburg, South Africa, having been postponed for a day.Second unit crews shot action sequences without the main cast, to be used as background plates for scenes featuring the Hulk, in the Central Business District of Johannesburg for a period of two weeks. By mid-March, principal photography had begun at Shepperton Studios near London and is scheduled to film there for at least four months. Filming at Shepperton as well as other locations in England allowed Whedon to get a "number of different looks and textures and moods" to give the film a different palette and fresh aesthetic from its predecessor. On March 22, production moved to Fort Bard, Italy and continued in the Aosta Valley region through March 28. The region doubled as Eastern Europe, with crews replacing local storefronts with Cyrillic script. Filming in South Korea began on March 30 on the Mapo Bridge and continued through April 14 at various locations in Seoul. An artificial island on the Han River known as the Saebit Dungdungseom served as the headquarters of an IT institute featured in the film. Scenes involving Ultron's attack on parts of the city were shot in the Gangnam District.
In February 2014, Industrial Light & Magic announced plans to open a facility in London, citing Avengers: Age of Ultron as a catalyst for the expansion. The IMAX release of the film will be converted to IMAX 3D.
In March 2014, Brian Tyler signed on to compose the film's score, replacing the composer for the first film, Alan Silvestri, while also marking his third film collaboration with Marvel following Iron Man 3 and Thor: The Dark World in 2013. Tyler intends to pay homage to John Williams' scores for Star Wars, Superman and Raiders of the Lost Ark, as well as reference the scores for Iron Man, Thor and Captain America "in order to create a similar musical universe."
At the 2013 San Diego Comic-Con International, Joss Whedon introduced a teaser trailer for the film, which included a look at an Ultron helmet and a title treatment. Footage of the teaser, as well as a brief interview with Whedon, was made available as part of Iron Man 3's second screen companion app for its Blu-ray release on September 24, 2013. On March 18, 2014, ABC aired a one-hour television special titled, Marvel Studios: Assembling a Universe, which included a sneak peek of Avengers: Age of Ultron. The special debuted concept art for Quicksilver and Scarlet Witch, as well as art of the Hulk fighting a "Hulkbuster"–like Iron Man suit.Harley-Davidson partnered with Marvel to provide their first electric motorcycle, Project LiveWire, for use by Black Widow in the film.
Avengers: Age of Ultron is scheduled for release in the United Kingdom and Ireland on April 24, 2015 and on May 1 in North America, in 2D and IMAX 3D.